1. Technical Field
The present invention relates to power stability control in wavelength division multiplexing networks and more particularly to a state-based method and system for controlling power stability in such networks.
2. Description of the Related Art
In recent years, reconfigurable optical add/drop multiplexers (ROADMs) have been widely deployed for their flexibility and their enablement of automated control and dynamic provisioning in wavelength division multiplexing (WDM) networks. Currently, most ROADMs utilize wavelength blockers (WB) or wavelength selective switches (WSS) to switch arbitrary wavelengths at a per-wavelength granularity. WE and WSS can attenuate an incoming wavelength for up to 10 to 15 dB at a step size as low as 0.1 dB. This feature of ROADMs is advantageous, as per channel power control and power equalization can be achieved without additional attenuators.
In a network including cascaded ROADMs and Erbium Doped Fiber Amplifiers (EDFAs), if an optical fiber transmission line is cut or some channels are dropped, the total number of channels in the network may change abruptly and may result in a power excursion to the remaining channels. All ROADM nodes in the network that detect the abnormal power level of a channel using an optical channel monitoring (OCM) module gradually adjust their attenuation for that channel so as to maintain its power level within a preset range. Usually, ROADM nodes adjust their attenuation independently without centralized coordination by means of an optical supervisory channel (OSC).
If the number of cascaded ROADMs is large enough, the independent attenuation could cause strong power ripples and oscillation in the transparent network. In addition, it takes a long time for the network to control the power and reach a stable condition within the present range. During the power control process, WDM signals experience frequent power variation that induces nonlinear effects in optical fiber transmission lines or exceeds the dynamic operable range of optical receivers. Therefore, signal quality is degraded during the transient period.